I started taking this about 6 months ago and I know now that I will take it for the rest of my life. As someone who suffers from allergies to several things, as well as chronically waking up in the morning with fairly restricted nasal passages, I now take one of these capsules (600 mg) as soon as I get up and within about 15 minutes I can breathe much easier. A terrific immune system booster also -- as cysteine is the rate-limiting precursor to glutathione, the body's main fuel for the I.S.
The label doesn't say this, but you should also take vitamin C at the same time -- not only for synergistic effect, but to prevent any possibility of kidney stones from long term use. I'd recommend 500 mg with each capsule taken. Like all amino acids, take on an empty stomach with water (ie. 30 minutes before a meal or 2 hours after). I'd also suggest methionine for those who experience high histamine levels.

I have been using various supplements to good effect, but Now NAC topped it off for me. I used to have low energy in the morning and hit lows in the late afternoons, but after taking this supplement, my mood has been centered, I feel better, and I look a little healthier.
It may have to do with my body blood type in that I do not make enough neurocrine hormones (adrenaline, dopamine, epinephrine, etc.) So, the selenium production/inclusion helps, as well the glutathione production is said to help with the liver healing, and joint mobility and is an antioxidant found in every cell of the body so helps with binding to free radicals inside the cells
In conclusion, it is working good for me so far.

I use Now Foods NAC because it increases my energy. NAC also naturally removes mercury from my body. It is said to cure cataracts. I stopped taking it for a month and my eyesight got worse. Since I found a source that I can get from Australia, I won't let myself run out of it again. Since starting it again, my eyesight seems to have gotten better.

Many good reviews here on this NAC product so I will keep it brief.
I take this as a Glutathione(aka GHS, a very potent antioxidant) booster. Oral Glutathione supplements don't work! Therefore by taking the precursor NAC you support your body to produce more of it.
I take one in the AM and one in the PM on an empty stomach. I like that this has some selenium in it. Just make sure your total selenium supplementation does not exceed 400 mcg per day.
L-Glutamine is another precursor to GHS and some people will also add that to their GHS boosting regiment.
Anyone with a health issue should consider boosting their GHS as they would likely benefit.
NOW makes quality products and this is a good value here on iherb for a 600mg vcap.
If you found this helpful kindly visit my iherb home page and see more value added reviews.
Peace and good health.

I use it for endometriosis and cysts. Cleans the liver efficiently, and helps with insulin resistance and PCOS. Also, it helps my husband increase sperm motility, as recommended by a physician. Used with l-glutamine, as precursors to Glutathione, the master antioxidant.

Excellent proven value. Used with a good candida plan including probiotics & Candida Support, NAC strengthens immunity to cope with candida die off. I am using this myself and recommending it to friends as I conquer my candida overgrowth. Start with a good candida diet then introducing NAC to build immunity. One week later add mixed probiotics. After another week add Candida support to kill off the Candida Albicans. You need this order to build immunity and good intestinal flora and cope with die off of Candida. Stay on all 3 supplements (and diet) for 2 months.

As a Hashimoto's sufferer, I often struggle with short-term memory and brain 'fog' issues. This supplement has had a notable effect in improving this for me. It has helped me get through a very complex research project that I was dreading. Initially I had a few minor headaches which I have read can be a side-effect, but these have settled down now. I usually also take my supplements only on weekdays and 'rest' my body on weekends. I will continue to take this for the longterm.